(For Firefox 4 only.)
This extension is very similar to another extension Packed Menu except that it puts the button on the Navigation Toolbar instead of the Menu Bar.
This extension conflicts with the extension Packed
Menu, so I self-host it. You must read this and uninstall Packed
Menu before you can use this extension.
This extension adds a button "M" to the Navigation Toolbar. And the original main menus are hidden. When you click the "M" button or press Alt-M, the original main menus are shown under the "M" button.
After the installation, the Menu Bar may become empty. You can choose to hide it by unchecking View|Toolbars|Menu Bar.
This extension has nearly no impact to the Firefox's performance. All it does is just adding a menu "M" to the tool-bar and moving the original "main menu bar" to the popup of the menu "M".
This extension can be downloaded and installed from: http://code.google.com/p/packed-menu-2-nav/
Install another extension Autohide Tabbar together and you would get a neater interface.